Department of Radiology, University of Pennsylvania, Philadelphia, PA 19104, United States.
J Magn Reson. 2013 Sep;234:90-4. doi: 10.1016/j.jmr.2013.06.008. Epub 2013 Jun 20.
Dynamic nuclear polarization (DNP) of (15)N2O, known for its long-lived singlet-state order at low magnetic field, is demonstrated in organic solvent/trityl mixtures at ∼1.5 K and 5 T. Both (15)N polarization and intermolecular dipolar broadening are strongly affected by the sample's thermal history, indicating spontaneous formation of N2O clusters. In situ (15)N NMR reveals four distinct powder-pattern spectra, attributed to the chemical-shift anisotropy (CSA) tensors of the two (15)N nuclei, further split by the intramolecular dipolar coupling between their magnetic moments. (15)N polarization is estimated by fitting the free-induction decay (FID) signals to the analytical model of four single-quantum transitions. This analysis implies (10.2±2.2)% polarization after 37 h of DNP, and provides a direct, instantaneous probe of the absolute (15)N polarization, without a need for time-consuming referencing to a thermal-equilibrium NMR signal.
在 ∼1.5 K 和 5 T 的条件下，在有机溶剂/三苯基甲烷混合物中证明了（15）N2O 的动态核极化（DNP），（15）N2O 以其在低磁场下长寿命单重态有序而闻名。（15）N 极化和分子间偶极展宽都强烈受到样品热历史的影响，表明 N2O 簇的自发形成。原位（15）N NMR 揭示了四个不同的粉末图案谱，归因于两个（15）N 核的化学位移各向异性（CSA）张量，进一步通过它们磁矩之间的分子内偶极耦合分裂。（15）N 极化通过将自由感应衰减（FID）信号拟合到四个单量子跃迁的分析模型来估计。这种分析意味着在 DNP 37 小时后达到（10.2±2.2）%的极化，并且无需耗时参考热平衡 NMR 信号，直接提供了绝对（15）N 极化的瞬时探针。
